Short-Term Amphibian Toxicity Tests and Paraquat Toxicity Assessment

Changes in agricultural practice may alter agrichemical effects on nontarget wildlife. Because of routine practice in various forms of conservation tillage, paraquat (1,1′-dimethyl-4,4′-bipyridinium dichloride) has increasingly been used for weed control in agricultural fields and in supporting management practices. Though highly adsorbed by soil and foliage, paraquat may gain increased notice as an agrichemical potentially impacting wetlands which surround much of the farmland across the country; consequently, amphibian toxicity evaluations may be incorporated into wildlife hazard assessments conducted for chemicals finding increased use in conservation tillage. Using amphibians representative of two anuran families, early life stage toxicity tests (96-h modified FETAX) were performed. Acute and subacute exposures were completed, and toxicity endpoints (mortality and teratogenicity) were evaluated for exposures to technical-grade and formulation-grade paraquat. These preliminary toxicity assessments suggested that acute and subacute endpoints for each form of paraquat may be significantly different, since the commercial formulation was three times as acutely toxic as the technical-grade chemical. Furthermore, it appeared that species and familial differences must be regarded with increased caution until a comparative toxicity data base is developed for amphibians.